Effect of atmospheric action center in low-frequency teleconnection mechanism: an explicit analytic study

In consideration of the characteristics of spectral average of the Rossby wave trains and the adoption of a climatic mean stream field as the basic stream field, an approximate analytical formula for the period of atmospheric low-frequency oscillation (LFO) and the group velocity is deduced from a barotropic and non-divergent linearized vorticity equation. All the action centers of atmosphere are found to be the oscillators of low frequency. The LFO propagates southward across the streamlines in the wind field with a southward component or propagates northward across the streamlines in the wind field with northward component instead of along a great circle. The switch of the propagation direction takes place near the top of ridge or the bottom of trough. The angle between the wave rays and the zonal direction can be determined. Project supported by the National Natural Science Foundation of China (Grant No. 49175241).     

Red giant stellar collisions in the Galactic Centre

We show that collisions with stellar-mass black holes can partially explain the absence of bright giant stars in the Galactic Centre, first noted by Genzel et al. We show that the missing objects are low-mass giants and asymptotic giant branch stars in the range  1–3 M_⊙  . Using detailed stellar evolution calculations, we find that to prevent these objects from evolving to become visible in the depleted K bands, we require that they suffer collisions on the red giant branch, and we calculate the fractional envelope mass losses required. Using a combination of smoothed particle hydrodynamic calculations, restricted three-body analysis and Monte Carlo simulations, we compute the expected collision rates between giants and black holes, and between giants and main-sequence stars in the Galactic Centre. We show that collisions can plausibly explain the missing giants in the  10.5 < K < 12  band. However, depleting the brighter  ( K < 10.5)  objects out to the required radius would require a large population of black hole impactors which would in turn deplete the  10.5 < K < 12  giants in a region much larger than is observed. We conclude that collisions with stellar-mass black holes cannot account for the depletion of the very brightest giants, and we use our results to place limits on the population of stellar-mass black holes in the Galactic Centre.     

The effectiveness of the Kozai mechanism in the Galactic Centre

I examine the effectiveness of Kozai oscillations in the centres of galaxies and in particular the Galactic Centre (GC) using standard techniques from celestial mechanics. In particular, I study the effects of a stellar bulge potential and general relativity on Kozai oscillations, which are induced by stellar discs. Löckmann et al. recently suggested that Kozai oscillations induced by the two young massive stellar discs in the GC drive the orbits of the young stars to large eccentricity  ( e ≈ 1)  . If some of these young eccentric stars are in binaries, they would be disrupted near pericentre, leaving one star in a tight orbit around the central supermassive black hole and producing the S-star population. I find that the spherical stellar bulge suppresses Kozai oscillations, when its enclosed mass inside a test body is of the order of the mass in the stellar disc(s). Since the stellar bulge in the GC is much larger than the stellar discs, Kozai oscillations due to the stellar discs are likely suppressed. Whether Kozai oscillations are induced from other non-spherical components to the potential (e.g. a flattened stellar bulge) is yet to be determined.     

GMRT observations of four suspected supernova remnants near the Galactic Centre

We have observed two fields – Field I     ,     and Field II     ,     – with the Giant Metrewave Radio Telescope (GMRT) at 330 MHz. In the first field, we have studied the candidate supernova remnant (SNR) G3.1−0.6 and, based on its observed morphology, spectral index and polarization, confirmed it to be an SNR. We find this supernova to have a double ring appearance with a strip of emission on its western side passing through its centre.
We have discovered two extended curved objects in the second field, which appears to be part of a large shell-like structure. It is possibly the remains of an old supernova in the region. Three suspected SNRs, G356.3−0.3, G356.6+0.1 and G357.1−0.2, detected in the MOST 843-MHz survey of the GC region appear to be located on this shell-like structure. While both G356.3−0.3 and G356.6+0.1 seem to be parts of this shell, G357.1−0.2, which has a steeper spectrum above 1 GHz, could be a background SNR seen through the region. Our H  i absorption observation towards the candidate SNR G357.1−0.2 indicates that it is at a distance of more than 6 kpc from us.     

基于服务元数据的资源注册中心设计与实现

本文基于OGC/CS-W规范,从元数据信息模型、数据库结构设计、接口规范以及权限控制和资源质量评价等方面出发,面向服务元数据的共享需求,设计并实现了一种既具有普适胜,又可进行个性化扩充的服务资源注册中心体系架构,为地理信息数据/服务的集成应用、共享与互操作提供了一种思路.     

Evaluation and rehabilitation of dam seepage problems. A case study: Kafrein dam

The intention of this study is to locate the probable sources of the Kafrein dam seepage problem. A methodology known as excitation-response analysis will be considered. Analytical expressions, depicting the groundwater level response in the underlying aquifer as a result of changes in the reservoir water level, were derived from a linearized groundwater flow equation for one-dimensional semi-infinite, isotropic and homogeneous porous media. The results revealed that a large proportion of the seepage water originates from a site at a distance about 1 km from the observation point M1 and streamlines along the existing faults. Emphasis in this work was also placed on controling and mitigating the seepage problem.     

应用GIS的城市中心区定界方法

城市中心区等空间范围是城市研究中必须面对的基本问题。由于社会经济要素集聚的相对性和过渡性,城市中心区的位置和界线范围通常是不明确的,只有一个大致的范围,缺乏一个简单的确定方法。依据市政公用设施、地价、交通量等统计数据及其空间分布确定城市范围的传统方法工作量大、欠缺可比性。本研究以广州市城市道路网为数据基础,利用ArcGIS空间分析的密度分析方法圈定并验证了广州市城市中心区的边界范围。     

The microlensing rate and mass function versus dynamics of the Galactic bar

With the steady increase of the sample size of observed microlenses towards the central regions of the Galaxy, the main source of the uncertainty in the lens mass will shift from the simple Poisson noise to the intrinsic non-uniqueness of our dynamical models of the inner Galaxy, particularly the Galactic bar. We use a set of simple self-consistent bar models to investigate how the microlensing event rate varies as a function of axis ratio, bar angle and velocity distribution. The non-uniqueness of the velocity distribution of the bar model adds a significant uncertainty (by about a factor of 1.5) to any prediction of the lens mass. Kinematic data and self-consistent models are critical to lift the non-uniqueness. We discuss the implications of these results for the interpretation of microlensing observations of the Galactic bulge. In particular we show that Freeman bar models scaled to the mass of the Galactic bulge/bar imply a typical lens mass of around 0.8 M⊙, a factor of 3–5 times larger than the value from other models.     

意大利撒丁岛中部Lasasai-Bonucoro地区的废弃露天滑石-绿泥石-长石采矿场的水资源及其修复模式

摘要在撒丁岛中部Orani地区,一些赋存在古生代变质岩和花岗岩中的滑石．绿泥石．长石矿体一直处于露天开采状态。采矿活动严重破坏了Lasasai-Bonucoro地区的原始景观。露天开矿形成了一些水坑,里面填满了来自含水层的沿断裂渗出水,因此对该地区的重整应被视作是对自然景观的全面修复工程。在本次工作的第一阶段,作者描述了环境和水文地质学特征,以及根据不同整治措施对不同地域进行了划分。随后的工作包括详细地解释不同的整治技术措施。为了使该地区复原,首要措施包括：1)对一些地形崎岖的地点进行平整改造和重新规划。也就是根据前期规划合适的地点,将矿石开采和堆存地中过多的废石搬走并回填到山谷中。2)修复被挪走的土壤植被,并且在完成污水处理之后,通过植被重植的方法(包括：移植土壤和养分、水流播种草本植物,阶段性机械洒水)对新形成的地表进行改造。3)并通过以上重植技术,修复恰当的斜坡以及总体缺乏植被的地表。以上措施会引起地表高度和地形的微小变化。可是这些措施足以形成一个新的环境条件,可进行新的开采。特定情况下,例如在有恒定的高品质水流,并且环境宜人的乡村,以上建议很容易实施。因而,Lasasai-Boalitynucoro地区的资源的可利用性至少包括以下互不相斥的两个方面：1)休闲胜地,2)矿泉水生产基地。通过以上方法,Lasasai-Bonucoro地区的环境修复将会产生新的经济、文化、娱乐和观光价值。